JP2000208146A - Electrochemical capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical capacitor of a low cost and a high capacity by carrying a ruthenium (IV) oxide on activated carbon. SOLUTION: In this electrochemical capacitor having a pair of electrodes 11 and 12, an ion permeable porous separator 15 disposed between the electrodes 11 and 12 for electronically insulating them and an electrolyte solution immersed in these, the pair of electrodes 11 and 12 are electrodes containing complex activated carbon fine particles manufactured by a process of neutralizing with an alkali after a halide of a transition metal element of Group VIII is immersed in activated carbon fine particles 13 and 14 from a water solution containing the halide of the transition metal element 6 Group VIII.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical capacitor which performs charging and discharging electrochemically.

[0002]

2. Description of the Related Art Generally, at an interface where a solid and a liquid come into contact, positive and negative charges are arranged to face each other at an extremely short distance to form an electric double layer. When a DC voltage is applied to the electric double layer, electric charges are stored in accordance with the voltage, and as a result, electric energy is stored. An electric double layer capacitor utilizing the capacitance of the electric double layer is known (for example, see Japanese Patent Application Laid-Open No. 9-129509).

[0003] The electric double layer capacitor utilizes the large surface area of activated carbon, and has begun to be used as an energy device such as a small-capacity battery in various home electric appliances, including memory backup of ICs. Recently, a capacitor having a larger capacity has been developed, and its application to a hybrid electric vehicle (HEV) has been promoted as a power capacitor capable of obtaining a high output at a low cost.

[0004]

However, an electric double layer capacitor utilizing the surface area of activated carbon has insufficient capacity per unit weight and unit volume for application to a hybrid electric vehicle (HEV). There is a problem that there is. In the same expression as the battery, the energy density (W
h / kg, Wh / l) are insufficient.

[0005] In order to improve the capacity shortage of such an electric double layer capacitor, development of an oxidation-reduction capacitor which performs charge and discharge by a high-speed oxidation-reduction reaction using ruthenium (IV) oxide or the like instead of activated carbon has been developed. (For example,
Electrochemical capasitors, FMDelnick et al. Edit
ors, Electrochemical Society PV 96-25, P.208, theE
electrochemical Society Proceedings series, Penning
ton, NJ (1997).). This redox capacitor is larger in capacity than an electric double layer capacitor, but materials such as Ru and Ir which are currently being developed are expensive.
There is a problem that the cost is increased if a capacitor is to be formed by itself. In addition, there is a concern that a large amount of Ru or Ir consumes resources.

Therefore, it is conceivable to increase the capacity of an activated carbon by supporting a redox capacitor material such as ruthenium (IV) oxide on the activated carbon while utilizing the capacity of the activated carbon. However, no practical method has been reported so far in which ruthenium (IV) oxide is supported on activated carbon of a capacitor electrode to increase the capacity of the capacitor.

The present invention has been made in view of such conventional problems, and provides a low-cost electrochemical capacitor having a large capacity, that is, a large energy density by supporting ruthenium (IV) oxide on activated carbon. The purpose is to do.

[0008]

In order to achieve the above-mentioned object, the present invention provides a pair of electrodes, an ion-permeable porous separator interposed between the pair of electrodes, and electrically insulated from the pair of electrodes. An electrochemical capacitor having an electrolyte solution, wherein the pair of electrodes is
VIII from aqueous solutions containing halides of group III transition metals
The above object is attained by providing an electrode containing composite activated carbon fine particles produced by a method characterized by absorbing a halide of a group transition metal element and then neutralizing the same with an alkali.

As the halide of the Group VIII transition metal element of the present invention, ruthenium trichloride can be preferably used. Further, the activated carbon fine particles used in the present invention have a surface area per unit weight and unit volume as large as possible, the capacity of the activated carbon itself is large, and the ruthenium oxide (IV) or the like is sufficiently used from the viewpoint that the original capacity is effectively used. Since it is effective to be able to maintain, the BET specific surface area is 1500 m ²
/ G or more and 3500 m ² / g or less are preferable. BE
If the T specific surface area is too large, the capacity per unit weight is large, but the capacity per unit volume is small, which is not suitable for applications where space is limited.

Still another feature of the present invention is that the activated carbon is allowed to absorb a halide of a group VIII transition metal element and then dried by heating, and a carrier such as ruthenium (IV) oxide is placed inside the activated carbon fine particles. It is for holding. The heating and drying temperature for this is preferably from 80 ° C to 200 ° C. If the drying temperature is too low, it takes time. If the drying temperature is too high, the activated carbon is ignited or some inconvenient substance is generated in the pores of the activated carbon, which causes a reduction in capacity.

According to the present invention, high-speed reactivity, which is important for the behavior of a capacitor of an oxidation-reduction substance, is maintained without sacrificing the original capacity of activated carbon as much as possible, and by making use of the surface area of activated carbon. It is intended to improve both the capacity per unit volume and the capacity per unit weight of the activated carbon electrode by effectively utilizing the voids that do not directly contribute to the carbon dioxide.

Hereinafter, the operation of the present invention will be described. According to the present invention, in addition to the capacity of the electric double layer on the surface of the activated carbon, a capacitance component developed by the presence of ruthenium (IV) oxide or the like sorbed on the activated carbon fine particles is added, so that a high-capacity and low-cost electrochemical capacitor is provided. Can be obtained.

As a method of increasing the capacitance of the capacitor, it is conceivable to physically mix a separately synthesized ruthenium (IV) oxide powder and activated carbon to form an activated carbon electrode. When the activated carbon synthesis supporting ruthenium (IV) oxide of the present invention is synthesized and compared with the case of the synthesis of ruthenium (IV) oxide, the size of the generated fine particles can be made the same as the activated carbon fine particle size. This process has the advantage that the process is simple and ruthenium is not easily lost.

Further, in the SEM image (reflection electron image in which the existence of the metal element is emphasized) on the surface of the activated carbon fine particles carrying ruthenium (IV) oxide, no lump of ruthenium (IV) is seen and ruthenium (IV) is This suggests that it is formed inside the fine particles. Therefore, there is a practically important merit that a minute short circuit or the like by a ruthenium (IV) oxide ultrafine particle through a separator hardly occurs.

Further, when capacitors are used by connecting them in series as in the case of an HEV, variation in capacitance between the capacitors becomes a serious problem. In the case of the capacitor using the activated carbon supporting ruthenium oxide (IV) according to the present invention, the distribution of ruthenium oxide (IV) in one capacitor electrode is smaller than that of the aforementioned physically mixed system of ruthenium oxide (IV) and activated carbon. There is an important advantage that it is easy in principle to make uniform between the positive and negative electrodes of one capacitor and between the electrodes of different capacitors.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an electrochemical capacitor according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view of an evaluation cell of an embodiment of the electrochemical capacitor according to the present invention.

First, the configuration will be described. The evaluation cell 10 of the electrochemical capacitor includes a positive electrode current collector 11 and a negative electrode current collector 12.
The space between the insulating rubber sheet 16 and the insulating rubber sheet 16 is partitioned by an ion-permeable porous membrane separator 15, and both sides thereof are filled with positive-electrode activated carbon fine particles 13 and negative-electrode activated carbon fine particles 14.

The porous membrane separator 15 electronically insulates between the positive electrode activated carbon fine particles 13 and the negative electrode activated carbon fine particles 14 and allows the permeation of ions. For example, a nitrocellulose membrane filter may be used. it can.

The positive electrode activated carbon fine particles 13 of this evaluation cell 10
The volume size of each of the negative electrode activated carbon fine particles 14 was a circle having a diameter of 12 mm and a thickness of 1 mm.

Activated carbon fine particles 13 and 14 of both positive and negative polarities are obtained from an aqueous solution containing a halide of a single or a plurality of Group VIII transition metal elements, and an activated carbon obtained by absorbing the halide of a single or a plurality of Group VIII transition metal elements. It is manufactured by neutralizing the fine particles with an alkali.

According to the present invention, the high-speed reactivity important for the capacitor behavior of the redox substance is maintained without sacrificing the original capacity of the activated carbon as much as possible and by utilizing the surface area of the activated carbon. The effective use of voids that do not directly contribute to the capacity of the electrode is to improve both the capacity as an activated carbon electrode, the capacity per unit volume, and the capacity per unit weight.

Hereinafter, embodiments of the electrochemical capacitor according to the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1 Ruthenium trichloride (RuCl)
Dissolve ₃ · 3H ₂ O) 0.1g of distilled water of about 50 ml, therein, BET specific surface area in addition 1g of activated carbon particles of 3000 m ² / g, was well shaken. Activated carbon settles out immediately, so it was shaken and stirred for a while for a while, and then left overnight. The supernatant was almost colorless and transparent. The activated carbon was filtered, air-dried, and further dried in a dryer at 120 ° C. for 12 hours. After cooling, the mixture was dispersed in about 50 ml of distilled water and neutralized by adding a small excess of sodium hydroxide solution while stirring with a magnetic rotator. After filtration, it was further washed with water, air-dried, and then dried in a dryer at 130 to 150 ° C. for 12 hours. A predetermined amount of the obtained sample was put into an agate mortar, weighed, and 5 mol / l of sulfuric acid was added thereto and mixed well to moisten the whole appropriately. This coarse paste was packed in the same amount into the activated carbon fine particles (13, 14) of the positive electrode and the negative electrode in FIG. 1 (each size was 12 mm in diameter and 1 mm in thickness), and the space between them was passed through a nitrocellulose membrane filter. The cell 10 was separated and configured to be appropriately pressed from above and below to perform a charge / discharge test. Note that a thin titanium plate was used as the positive and negative electrode current collectors.
The charge and discharge are performed between 0 and 0.7 V, and the current value is 10 m
A. The capacity of the cell was determined by dividing the amount of discharge electricity by the discharge section voltage, and was calculated as the capacity per unit weight of activated carbon in Table 1.
Shown in The capacity of the cell can be regarded as a relative value of the capacity per unit volume of the electrode.

Example 2 A cell 10 was constructed in the same manner as in Example 1 except that the weight of ruthenium trichloride (RuCl ₃ .3H ₂ O) was changed to 0.2 g, and a charge / discharge test was performed. . Table 1 shows the results.

Example 3 In Example 1, the weight of ruthenium trichloride (RuCl ₃ .3H ₂ O) was 0.05 g.
The cell 10 was constructed in the same manner, except that the charge / discharge test was performed. Table 1 shows the results.

(Comparative Example 1) In Example 1, the cell 10 was used as it was without carrying ruthenium (IV) oxide on activated carbon.
And a charge / discharge test was performed. Table 1 shows the results.

Example 4 A cell 10 was constructed in the same manner as in Example 1 except that the activated carbon fine particles having a BET specific surface area of 3000 m ² / g were changed to activated carbon fine particles having a BET specific surface area of 2000 m ² / g. A charge / discharge test was performed.
Table 1 shows the results.

(Comparative Example 2) In Example 4, the cell 10 was used as it was without supporting ruthenium (IV) oxide on activated carbon.
And a charge / discharge test was performed. Table 1 shows the results.

Example 5 A cell 10 was constructed in the same manner as in Example 1 except that the activated carbon fine particles having a BET specific surface area of 3000 m ² / g were changed to activated carbon fine particles having a BET specific surface area of 1700 m ² / g. A charge / discharge test was performed.
Table 1 shows the results.

(Comparative Example 3) In Example 5, the cell 10 was used as it was without supporting ruthenium (IV) oxide on activated carbon.
And a charge / discharge test was performed. Table 1 shows the results.

Comparative Example 4 A cell 10 was constructed in the same manner as in Example 1 except that the activated carbon fine particles having a BET specific surface area of 3000 m ² / g were changed to activated carbon fine particles having a BET specific surface area of 1000 m ² / g. A charge / discharge test was performed.
Table 1 shows the results.

[0032]

[Table 1]

As is clear from Table 1, in Examples 1, 2 and 3 of the present invention, the capacity of the cell, that is, the capacity per unit volume and the capacity per unit weight were clearly increased as compared with Comparative Example 1. ing. Example 4 of the present invention is comparative example 2
On the other hand, similarly, both the capacity per unit volume and the capacity per unit weight are clearly increased. Further, in Example 5 of the present invention, both the capacity per unit volume and the capacity per unit weight are clearly increased as compared with Comparative Example 3. Finally, Comparative Example 4 is based on Examples 1 to 5. In order to increase the capacity per unit volume and the capacity per unit weight, it is effective to use activated carbon having an appropriate BET specific surface area. Is shown.

[0034]

As described above in detail, according to the present invention, in addition to the capacity of the electric double layer on the surface of activated carbon, the capacity developed due to the presence of ruthenium (IV) oxide and the like sorbed on the activated carbon fine particles. Since the components are added, a high capacity and low cost electrochemical capacitor can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an evaluation cell of an embodiment of an electrochemical capacitor according to the present invention.

[Explanation of symbols]

 Reference Signs List 10 evaluation cell 11 positive electrode current collector 12 negative electrode current collector 13 positive electrode activated carbon fine particles 14 negative electrode activated carbon fine particles 15 ion permeable porous membrane separator 16 insulating rubber sheet

Claims (4)

[Claims] 1. An electrochemical capacitor having a pair of electrodes, an ion-permeable porous separator interposed therebetween and electrically insulating, and an electrolyte solution contained therein, wherein the pair of electrodes comprises: Activated carbon fine particles, from an aqueous solution containing a halide of a Group VIII transition metal element, composite activated carbon fine particles produced by a method characterized by neutralizing with alkali after absorbing the halide of the Group VIII transition metal element An electrochemical capacitor, comprising: 2. The electrochemical capacitor according to claim 1, wherein the halide of the Group VIII transition metal element is ruthenium trichloride. 3. The electrochemical capacitor according to claim 1, wherein the activated carbon fine particles have a BET specific surface area of 1500 m ² /
electrochemical capacitor which is a mixture of g to 3500 m ² / g or less in single or this condition is satisfied charcoal. 4. The electrochemical capacitor according to claim 1, wherein the composite activated carbon fine particles are activated carbon particles having absorbed the halide of the Group VIII transition metal element at a temperature in the range of 80 ° C. to 200 ° C. An electrochemical capacitor comprising activated carbon fine particles produced by a method of heating and drying and then neutralizing with an alkali.